1. Technical Field of the Invention
This invention relates to a machining quality judging method for a wafer grinding machine and wafer grinding machine.
2. Description of the Related Art
With an ever-increasing trend toward higher integration and packaging of semiconductor devices in recent years, semiconductor chips (dies) have been correspondingly reduced in thickness. As a result, the back surface of the wafer is ground by a grinding means before dicing. During the wafer back surface grinding process, the front surface of the wafer is protected by a protective tape attached thereon.
Further, it has become common practice to polish the back surface of the water that has been ground to remove distortion.
In the case where the wafer blank is hard and difficult to grind, for example, a grinding defect such as “surface burn” or “burr” may be caused, thereby making the desired grinding process difficult.
In view of this, Japanese Unexamined Patent Publication No. 2007-301665 proposes a grinding wheel having a grinding stone formed of a resin bonding agent mixed with abrasive diamond grains and micro metal balls.
The metal balls, which contact other objects comparatively softly, function as a buffer between the abrasive diamond grains and the wafer and has a cooling function due to the high heat conductivity on the other hand. These functions, coupled with the cutting function generated by the spherical metal balls dropping off which in turn causes the drop-off of the diamond abrasive grains, can contribute to an efficient grinding operation for the wafer of a hard-to-grind material without surface burn and burring.
Japanese Unexamined Patent Publication No. 2007-301665, does not disclose that the back surface of the wafer is monitored to execute the desired grinding process.
In the case where undesired grinding continues, a product defect cannot be avoided and yield is reduced.